The llvm.lifetime.start intrinsic guarantees that the address for a
given alloca is always the same. So variables with escaped addresses
reaching reaching a lifetime start/end block before and after a suspend
must be placed onto the coroutine frame even if the variable itself
is not alive across the suspend point.
This computes a new `LoopKill` flag in the suspend crossing data flow
anaysis to catch the case where a lifetime marker can reach itself
via suspend-crossing path.
This fixes https://llvm.org/PR52501
Differential Revision: https://reviews.llvm.org/D140231
ae7bf2b80b